The drill bit is a critical component in oil, gas, and geothermal drilling. The drill bit is fitted to the end of a drill string, and a working face of the drill bit typically comprises tungsten carbine or diamond coated surfaces that cut and chip subterranean formations. The drill pipe and drill collars are positioned above the drill bit to steer and direct the drill bit as the drill string is pushed into the earth. Accordingly, the cross sectional area or outer diameter of the working face of the drill bit is larger than the cross sectional area or outer diameter of the other components in the drill string. Otherwise, these components would not fit down the wellbore as the drill string is pushed into the earth, and the drill string could become stuck in the wellbore at significant expense.
Once a wellbore is drilled, a casing is typically lowered into the wellbore and cemented in place to help preserve the integrity of the wellbore against collapse, and more importantly to isolate the wellbore from various oil and gas reservoirs and water aquifers. Production tubing may be run internally through the casing string to provide a constant and continuous bore from the production zone to the wellhead.
Historically, wellbores were drilled in a substantially vertical direction or at a moderate angle below the surface location. However, the advent of horizontal drilling has changed this paradigm. With horizontal drilling, a drill string and the resulting wellbore can change directions. For example, at a given depth, the drill string and the wellbore may be oriented substantially horizontally. Horizontal drilling provides many benefits including increasing the exposure of the well to a reservoir over an extended distance, grouping wellheads at a central location to reduce the surface area or footprint needed to conduct drilling operations, and drilling underneath natural and man-made obstacles.
Hydraulic fracturing is another technology that has improved the production of oil and gas wells. Hydraulic fracturing is a process where fluid and sand or ceramic beads are pumped down into the wellbore at very high pressures. The interaction between the high pressure fluid and the target subterranean formation fractures rock, which creates cracks and fissures that release oil and gas. The combination of horizontal drilling and hydraulic fracturing has led to a renaissance in North American oil and gas drilling and significant increases in production and ultimate hydrocarbon recovery.
In some North American shale reservoirs, e.g., the Bakken and Marcellus reservoirs, hydraulic fracturing is performed in substantially horizontal wellbores at predetermined production intervals. Fracturing plugs are set at various points in the wellbore to temporarily seal off intervals for hydraulic fracturing treatment. Once the hydraulic fracturing is performed, a drill bit with a working face is used to drill through the fracturing plug and provide access to the recently-treated interval.
An issue with drilling through a fracturing plug is that the working face of the drill bit and the overall bit housing diameter are smaller than the cross sectional area or inner diameter of the casing or tubing that the fracturing plug is positioned in. In addition, the cross sectional area and/or outer diameter of the working face or housing of the drill bit is larger than the other components of the drill string, which is the standard or norm during drilling. Within a horizontal or deviated wellbore, this results in the drill bit contacting and wearing against one side of the casing or tubing. Since wellbores may be miles long, this contact can lead to premature wearing of the working face of the drill bit and other components of the drill bit such as the shank of the drill bit.
Another issue is that once the drill bit reaches the fracturing plug, the drill bit is not aligned with the fracturing plug to properly drill out the fracturing plug. More specifically, fracturing plugs are typically made from plastic and composite materials which are designed to be frangible and drilled out after serving their useful purpose. Fracturing plugs are optimally drilled through the center of the fracturing plug so that the fracturing plug is reduced to many small pieces and returned to the surface. However, with currently existing drill bits and drill strings, the drill bit is ineffectively aligned with one edge of the fracturing plug positioned on the low side of a deviated wellbore. Thus, the resulting drilling operation of the fracturing plug is ineffective and inefficient, taking additional time and adding expense to the wellbore operation.
These deficiencies, among others, are addressed in the present invention described in detailed below.